Shaving heads of the type initially referred to are known for example from EP 0693988 B1. This document discloses an electric dry shaver where a center trimmer is arranged between two foil type shaving elements. The upper cutter of this center trimmer is provided with hair feeding means consisting of projecting teeth which are directed outwardly. Those center trimmers in general are rather effective in cutting the hairs to a very short remaining length of hair. With respect to hairs which are resting flat against the skin the performance of the known cutting system is not optimal since such hairs—especially if they are located on skin areas with flexible skin—tend to escape from the feeding area formed between two teeth of the comb-shaped feeding means.
From the EP 1930135 A1 there is known a shaving head with three foil-type cutters and a center trimmer which comprises a multiplicity of bars arranged at a small distance to each other, so as to form small slits between the bars. Such kinds of center trimmers are a more open construction without a center bar arranged along the longitudinal axis of the trimmer. Cutting units of this type have proven to be mechanically stable even with a small thickness of the outer cutter. The drawback of this kind of shaving units is the risk to cause skin irritations. The center trimmer according to the EP 1930135 A1 acts to the hairs like an expanded comb when moved during a shaving stroke along the skin. The hairs will then be directed accordingly. However, hairs to be cut have to pass completely through the height of the outer cutter of the center trimmer which most likely will not happen to hairs lying flat to the skin.